As described in applicant's U.S. Pat. No. 4,517,778, the San Francisco North Quadrangle lies between the active San Andreas and Hayward faults and is within a region of high seismic activity in which earth tremors are frequent and unpredictable. For example, the infamous 1906 earthquake in San Francisco has been extensively documented in many publications, including publications authored by H.O. Wood. The relationship between damage to man-made building structures, foundations, and geology was investigated by Wood, who found that damage to structures was primarily influenced by the constituent makeup of their foundations. Further studies have concluded that the natural periods of vibration of the foundation and the supported structure, as well as the nature of the earthquake vibration and the foundation material, must be considered in the design and construction of buildings and the like.
Wood thus concluded that damage to building structures in the 1906 earthquake were primarily occasioned by the foundations of the buildings. Buildings situated on bedrock and on well-designed and well-placed piles or concrete footings, were found to suffer less damage than buildings erected on soft foundations in landfill areas.
Studies of the above type have given rise to modern-day building techniques, including the driving of piles or support columns into solid ground to support a building structure. However, since the building structure is integrally connected to the foundation and thus the ground proper, vertical, horizontal, and/or inclined faulting will transmit seismic forces to the building structure directly, regardless of the type of foundation and ground makeup.